The present invention relates to magnetic heads useful as reading heads for magnetic media such as magnetic disks, magneto-optical disks and magnetic tapes. In particular, the present invention relates to magnetic heads using magnetoresistive devices in which current flows perpendicularly to the film plane via a non-magnetic layer, such as a magnetoresistive device using a tunneling magnetoresistive effect (TMR device) and a magnetoresistive device using a giant magnetoresistive effect of the current perpendicular to the plane type (CPPGMR device).
In order to deal with increasing magnetic recording densities, spin-valve type GMR devices are beginning to be put into use. The principle of the spin-valve type GMR devices is explained based on changes in the mean free path of electrons traveling in the direction along the film plane (inplane direction), depending on the angle formed by the magnetization directions of the free layer and the pinned (fixed) layer. The spin-valve type GMR device has achieved a MR ratio (magnetoresistance ratio) of about 10%, which is several times higher than that of conventional anisotropic MR devices.
On the other hand, TMR devices are under development as a material that can provide even higher MR ratios. TMRs utilize the tunnel transition probability that varies with the angle formed by the magnetization directions of two ferromagnetic layers via a non-magnetic tunnel layer. In the TMR devices, unlike the spin-valve type GMRs, current flows in the direction across the film plane (direction perpendicular to the plane).
The following structures of magnetic heads using the TMR devices have been proposed. JP11-213349A discloses a magnetic head having a structure in which a MR device portion of a shield type MR head used in conventional GMR heads is replaced by a TMR device, and a flux guide is provided. JP11-25425A discloses a magnetic head having a structure where a yoke is provided such that the yoke plane is perpendicular to the surface of the substrate, and a TMR device is provided in the yoke. In this magnetic head, the yoke is formed on the substrate, and the magnetoresistive device is provided on a part of the yoke.
It is an object of the present invention to provide a magnetic head having a structure suitable for a magnetoresistive device (magnetoresistive effect device) in which current flows perpendicularly to the film plane, such as a TMR device. It is another object of the present invention to provide a magnetic head having improved characteristics that can be achieved by improving the magnetoresistive device in which current flows perpendicularly to the film plane.
A magnetic head of the present invention includes a magnetoresistive device in which current flows in a direction perpendicular to a film plane. Basically, the magnetic head of the present invention includes a magnetoresistive device including a laminate structure in which a non-magnetic layer is interposed between a first magnetic layer and a second magnetic layer; a yoke for introducing an external magnetic field from a magnetic gap to the magnetoresistive device; a current introducing part for allowing current to flow between the first magnetic layer and the second magnetic layer via the non-magnetic layer; a measuring part for detecting a change in resistance occurring between the first magnetic layer and the second magnetic layer in accordance with a relative magnetization angle between the first magnetic layer and the second magnetic layer that is changed by the external magnetic field induced via the yoke; and a substrate over which the magnetoresistive device and the yoke are formed.
A first magnetic head of the present invention is characterized in that when the area of the non-magnetic layer is defined as a device cross-section area and the area of the yoke is defined as a yoke area, viewed along a direction perpendicular to a surface of the substrate, then the device cross-section area is not less than 30%, preferably not less than 50% of the yoke area.
In the magnetoresistive device in which current flows in a direction perpendicular to a film plane, unlike a device in which current flows along an inplane direction, an increase of the device resistance involved in achieving compactness of the device may deteriorate the characteristics of the head easily. In the first magnetic head, the increase of the device resistance is suppressed by making the ratio of the device cross-section area to the yoke area larger than that of conventional magnetic heads. When the device cross-section area is restricted to be as small as not more than 0.1 xcexcm2, the large ratio provides a large effect, although there is no particular limitation regarding the device cross-section area.
Furthermore, the first magnetic head of the present invention can achieve a short magnetic path length by which slight magnetic flux leaked from an ideal bit can be introduced to the yoke sufficiently. In order to introduce the magnetic flux sufficiently, it is preferable that the yoke height is not more than 10 xcexcm. Furthermore, in the first magnetic head, the ratio of the device cross-section area to the yoke area is large, and therefore the shape anisotropic effect of the yoke that causes the magnetic domains to block each other can be reduced, so that stable outputs can be obtained.
A second magnetic head of the present invention is characterized in that the magnetoresistive device is formed on the substrate, and the yoke is provided above the non-magnetic layer constituting the magnetoresistive device.
Conventionally, the yoke is formed on the substrate, and the magnetoresistive device is formed on the yoke (see JP 11-25425A). However, in the second magnetic head, the magnetoresistive device is provided between the substrate and the yoke, so that a region in which the device is to be formed can be obtained without being limited by the shape of the yoke and the increase of the device resistance can be suppressed. The second magnetic head is particularly suitable for a magnetic head having a form in which the yoke plane is substantially perpendicular to the surface of the substrate.
In the specification of the present invention, xe2x80x9csubstantially perpendicularxe2x80x9d refers to an angle in the range of 90xc2x0xc2x120xc2x0, and xe2x80x9csubstantially parallelxe2x80x9d refers to an angle in the range of 0xc2x0xc2x120xc2x0. Furthermore, xe2x80x9capproximately perpendicularxe2x80x9d refers to an angle in the range of 90xc2x0xc2x130xc2x0.
A third magnetic head of the present invention is characterized in that a magnetic layer that is either one selected from the first magnetic layer and the second magnetic layer and in which magnetization rotation is caused more easily by external magnetization than in the other magnetic layer (so-called free layer; the other layer is a pinned layer) comprises at least two magnetic films and at least one non-magnetic film that are laminated alternately, and the thickness of the non-magnetic film is not less than 2 nm and not more than 10 nm.
If the thickness of the non-magnetic film is in the above-described range, magnetostatic coupling is dominant between the pair of magnetic films that are laminated via this layer. Therefore, in the third magnetic head, the magnetic domains are stabilized, so that in the free layer, magnetization rotation is caused even more easily by an external magnetic field. Thus, the head characteristics are improved.
A fourth magnetic head of the present invention is characterized in that at least one magnetic gap is formed between a part of the yoke provided so as to constitute at least a part of one magnetic layer selected from the first magnetic layer and the second magnetic layer and the remaining part of the yoke, and the one layer is a magnetic layer (free layer) in which magnetization rotation is caused more easily by external magnetization than in the other magnetic layer. Furthermore, the free layer comprises at least two magnetic films and at least one non-magnetic film that are laminated alternately, the pair of adjacent magnetic films are coupled antiferromagnetically via the non-magnetic film, and the magnetic moment is not closed in the at least two magnetic films.
When a part of the yoke also functions as the magnetoresistive device, and a magnetic gap is formed between the magnetoresistive device and the remaining part of the yoke, the shape anisotropic effect of the yoke can be reduced. However, at the same time, the formation of the magnetic gap increases the demagnetizing field and reduces the magnetic flux induced to the device, because the magnetoresistive device is separated from the yoke. Therefore, in the fourth magnetic head, at least two magnetic films are coupled antiferromagnetically so that the effective magnetic moment is reduced. However, when the magnetic moments are completely canceled (namely, the magnetic moment is closed between the magnetic films), the magnetization rotation in the free layer hardly is generated. Therefore, the magnetic films preferably are coupled antiferromagnetically to each other to an extent that allows the magnetic moment to leak to the outside. The thickness of the non-magnetic film suitable for antiferromagnetic coupling is smaller than that suitable for magnetostatic coupling, and preferably is not less than 0.2 nm and not more than 1.0 nm.